Field of the Invention
The present invention relates to an X-ray Talbot capturing apparatus using a Talbot interferometer or Talbot-Lau interferometer.
Description of Related Art
There is an X-ray capturing apparatus which uses a Talbot interferometer or Talbot-Lau interferometer and a radiation detector (Flat Panel Detector: FPD) to capture and image a phase shift of an X-ray generated when the X-ray passes through an object (For example, Japanese Patent Application Laid-Open Publication No. 2007-206075, Japanese Patent Application Laid-Open Publication No. 2012-13530). Such X-ray image capturing apparatuses which use the Talbot interferometer or Talbot-Lau interferometer is called a X-ray Talbot capturing apparatus.
The X-ray Talbot capturing apparatus includes a first grating (also called G1 grating, etc.) and a second grating (G2 grating, etc.) provided with slits at a certain interval (when the Talbot-Lau interferometer is used, a ray source grating (G0 grating, multi gratin) is also included). The second grating is positioned in the position where a self-image of the first grating is focused at a certain interval downstream of the X-ray irradiating direction of the first grating by emitting the X-ray to the first grating from the X-ray source. The second grating is positioned so that the extending direction of the slit in the second grating is slightly tilted with respect to the extending direction of the slit in the first grating. With this, a moire fringe is formed on the second grating. The image with the moire fringe superimposed (hereinafter referred to as moire image) is detected with the X-ray detector positioned downstream of the second grating and captured.
When the subject is positioned between the X-ray source (or ray source grating) and the first grating or the first grating and the second grating, the moire fringe is distorted by the subject. Therefore, a plurality of moire images are captured with the X-ray Talbot capturing apparatus while relatively moving the first grating and the second grating (fringe scanning method) and then image processing is performed to analyze the moire images to reconstruct and generate images such as a differential phase image, absorption image, small angle scattering image, etc. Alternatively, one moire image including the subject can be captured with the X-ray Talbot image capturing apparatus, and the image processing can be performed to perform Fourier transform on the moire image to reconstruct and generate the differential phase image (Fourier transforming method).
In the X-ray Talbot capturing apparatus, the radiation irradiated from the radiation source (or the radiation which is irradiated from the radiation source and passes the ray source grating) normally spreads in a cone beam shape, and when the grating is formed in a flat plane shape, the problem of vignetting occurs in the periphery of the grating. In other words, although illustration is omitted, when the slit S of the grating (see later described FIG. 3) is formed to pass radiation entering the radiation entering surface of the grating in the normal vector direction, the radiation enters the radiation entering surface in a direction tilted with respect to the normal vector direction in the periphery of the grating. Therefore, the rate of passing of the radiation becomes worse in the periphery of the grating than the center of the grating.
Therefore, for example, Japanese Patent Application Laid-Open Publication No. 2007-206075, Japanese Patent Application Laid-Open Publication No. 2012-13530 describe a configuration in which the first grating and the second grating (or ray source grating) are curved. In other words, according to the method shown in FIG. 6 of Japanese Patent Application Laid-Open Publication No. 2007-206075 both edges of the grating are pressed in a direction toward the radiation source, the inner side is pressed in the opposite direction, and the grating is curved. According to the method shown in FIG. 7 of Japanese Patent Application Laid-Open Publication No. 2007-06075, with both edges of the grating fixed, the pressure applied to the radiation entering surface of the grating is set differently from the pressure applied to the radiation exiting surface (surface opposite of the radiation entering surface) to bend the grating.
According to Japanese Patent Application Laid-Open Publication No. 2012-13530, a plurality of plate shaped small gratings are aligned and placed between a first and second supporting substrate to form a combined grating plate. The combined grating plate is placed between a concave surface stage and a convex surface stage to bend the combined grating plate. According to the above configuration, the radiation enters the radiation entering surface in the normal vector direction in any portion of the radiation entering surface of the grating in the bent combined grating plate. Therefore, this prevents vignetting.
However, when the grating is formed with a hard material such as a silicon wafer, if the method shown in FIG. 6 of Japanese Patent Application Laid-Open Publication No. 2007-206075 is employed, strong force needs to be applied to the grating to bend the hard grating. However, if both edges of the grating and points on the inside are pressed with such strong force (in other words, contact by point), the grating may break and be damaged. If the method shown in FIG. 7 of Japanese Patent Application Laid-Open Publication No. 2007-206075 is employed, it is necessary to form a space with high airtightness and then vacuum the space in at least one side of the grating, which is not practical.
According to the method described in Japanese Patent Application Laid-Open Publication No. 2012-13530, a plurality of small gratings are placed between the first and second supporting substrates to form one combined grating plate, and the radiation is absorbed by the first and second supporting substrates. Therefore, the signal value of the differential phase image, etc. reconstructed and generated from the moire image captured as described above reduces and the S/N ratio of the differential phase image becomes worse.
Therefore, in the X-ray Talbot capturing apparatus, it is preferable to form the first grating and the second grating (or the ray source grating) by bending one flat plate grating formed with silicon wafer or the like. Moreover, it is desired that the damage due to breaking does not occur, the radiation is not blocked by the members other than the grating and the grating is accurately bent at a certain curvature.